The present invention relates to a bearing apparatus and a producing method thereof, and more particularly, to a bearing apparatus and a producing method thereof which are preferably used for a hub unit for a vehicle such as an automobile.
A hub unit for a vehicle will be explained. The hub wheel has a hollow shaft. An inner ring of a rolling bearing is mounted to an outer periphery of the hollow shaft by press-fit. A shaft end of the hollow shaft is caulked on the outer end surface of the inner ring by bending the shaft end outwardly in a diametrical direction. The bearing is prevented from slipping off from the hollow shaft by this caulked portion. A pre-load is applied to the inner ring of the bearing by this caulking.
A load is applied to the hollow shaft by the pressure-fit of the inner ring of the bearing. The hollow shaft is formed around its outer periphery with a hardened layer due to heat by quenching or the like in order that the hollow shaft has the structure that can bear the load. On the other hand, the shaft end of the hollow shaft remains in a stage of being caulked on the outer end surface of the inner ring, i.e., the shaft end is not hardened.
A range of the hardened layer formed on the outer periphery of the hollow shaft is limited to a certain degree.
However, in the range where the hardened layer is formed, a position of the caulked side end portion in the axial direction is not clearly defined. Thus, when it is processed to be hardened, the position of the caulked side end portion of the hardened layer in its add is prone to be an incorrect position closer to an outer end or to inner end in the axial direction from the limited range.
If the position of the end portion in the axial direction of the hardened layer is positioned incorrectly with respect to the hollow shaft, a gap may be generated between an inner peripheral surface of the inner ring and an outer peripheral surface of the hollow shaft caulked on the outer end surface thereof in some cases. This gap deteriorates creep resistance.
Therefore, a caulking auxiliary jig is previously inserted on the side of the inner periphery of the hollow shaft before caulking, thereby preventing the gap from being generated. Further, after the caulking, the inner periphery of the hollow shaft is again worked. Such a gap-preventing operation of the hollow shaft increases the number of producing steps and cost of the hub unit.